Now, the author and date information will not be displayed for the corresponding content type.

How about if you want to display the date information but not the author information, e.g. you want to see something like:

Posted: February 23, 2011

To accomplish this,

1. Enable Display Settings for the corresponding content type.
2. Edit the node.tpl.php file of the corresponding theme you are using, e.g. themes\bartik\templates\node.tpl.php and located the following command:print $submitted;

btw I just came across the Display Suite module which changes the "manage display" page to allow exactly for that and moving title, links, comments and way more useful features like changing/resetting field and views templates, linking between displays, dynamic & block fields, moving fields to a block just to name a few. Imho could replace views in those cases where you mainly use views to have more control over the output...

i answer to myself : there is nothing easier ... when you are using another language !!!

you go in site building / translate interface / search
and you search :
string contains : -->"Posted*" (* the translated term in the other language you use)
in "Built-in interface" you find your text
you edit and you find :
"Submitted by !username on @datetime" (translated)
you suppress the one you don't want anymore, register : it's ready !

I did it with CSS by using a new style for the content type's class. I tried Display Suite but couldn't find a the place to configure the author/date for my custom content type. Anyway, maybe I'll try it later with Panels...

You can customize those parts to change the wording "Submitted by", or only display the username or date. The following examples are using the template.php approach. For the node.tpl.php format, you would change $variables['myvariablename'] to $myvariablename.

(and of course you can change the string "Submitted on" to whatever you like.)

To customize the date format, the recommended solution is to use one of the predefined formats under Configuration > Regional and Language > Date and Time (Drupal 7.x) or Site Configuration > Date and Time (Drupal 6.x). Once this is done, you can then use those predefined formats in your code with format_date(). Refer to the Drupal API for full details on the format_date() function.

There is a MUCH easier way to do this. After searching for days and 2 bottles of Excedrin, one VERY simple solution is to simply reset the display for the comments. Then you can enable the field for the submitted by and position it above the comment field. You also have the option of hiding the label so that it doesn't show the Submitted by, unless you want to see it of course. There are a lot of other fields that you can add as well. It's all a matter of choosing which fields match your criteria.